A high melting metal such as tungsten and molybdenum is formed into projections and an electric field is applied to the ends of the projections in a vacuum from the outside, so that electrons induced to the ends of the metal are emitted to the outside. Generally, the metal projections are called emitters and the emission of electrons from the emitters is called field emission or field radiation.
Elements for emitting electrons to the outside through the field emission are called field-emission electron source elements or cold-cathode electron source elements and have been recently used in various fields. For example, the elements are used as the electron sources of electron microscopes instead of hot filaments of the related art, and are used for fluorescent display tubes in which light is emitted from phosphors by drawing electrons to an anode electrode on which phosphor films are formed so as to be opposed to electron source elements.
Generally, emitters have small structures and a single emitter cannot obtain a sufficient amount of current. Thus a group of emitters is used to obtain a sufficient amount of current. In the present specification, a group of emitters is called “cold-cathode electron source elements”.
Further, field emission displays (FEDs) have become practical in which cold-cathode electron source elements are arranged in a matrix to constitute a cold-cathode electron source array, an anode electrode on which phosphors corresponding to red, green, and blue are formed is disposed on the opposed side, and electrons through field emission are drawn to the anode electrode so as to emit light from the phosphors. The following will describe, as an example, an FED using Spindt-type emitters shown in FIG. 3.
The FED is configured such that a cathode substrate 101 and an anode substrate 111 are opposed to each other. On the surface of the cathode substrate 101, strip emitter address signal wires 102a are formed in parallel and a gate insulating film 103 is formed over the emitter address signal wires 102a. On the surface of the gate insulating film 103, strip gate signal wires 104a are formed so as to cross the emitter address signal wires 102a. 
On the gate signal wires 104a and the gate insulating film 103, a plurality of openings are formed in an area where the gate signal wires 104a and the gate insulating film 103 cross the emitter address signal wires 102a. In the respective openings, emitters 102b are formed so as to be disposed on the emitter address signal wires 102a. At this point, the openings on the surfaces of the gate signal wires 104a act as gate electrodes 104b. An electric field is applied to the gate electrodes 104b through the gate signal wires 104a, so that electrons can be emitted from the ends of the emitters 104b. An area where the emitters 104b and the gate electrodes 104b are formed is called a cold-cathode electron source element area.
Over a surface of the anode substrate 111, an anode electrode (not shown) of a transparent conductive film is formed such that the anode electrode faces the cathode substrate 101. On the anode electrode, phosphors 113R, 113G, and 113B of red, green, and blue are sequentially formed in strips. The phosphors are formed in parallel with the gate signal wires formed on the cathode substrate 101.
Electron emission from the electron source elements arranged in a matrix is sequentially controlled by a video circuit, achieving video display elements that display a desired image with light emitted from the phosphors. The light is emitted by the electrons received on the anode electrode having been fed with a voltage.
In the same configuration, by forming a photoelectric conversion film on the surface of the anode electrode, the electron source elements can be also used as image elements for reading hole-electron pairs, which have been induced by external light, by electrons emitted from the electron source elements.
In recent years, FEDs and image elements have had higher resolutions and a larger number of pixels have been demanded. As in LCDs (Liquid Crystal Displays) and PDPs (Plasma Display Panels), FEDs have been severely inspected for defects. Products with line defects appearing like lines are not valuable at all, and thus it is necessary to reduce the defects to at least point defects that appear within pixels.
Generally, electron source elements arranged in a matrix have a so-called simple matrix configuration in which pixels are connected to two intersecting signal wires and the electron source elements are operated by generating a predetermined potential at the intersections of the signal wires.
In the simple matrix configuration of the related art, however, a short circuit at the intersection between the wires may prevent the passage of the predetermined potential over the wires, so that all of the pixels connected to the wires may become inoperable and cause line defects. As a solution to the line defects, an excessive current flowing into a short-circuit point is limited to suppress a voltage drop on the signal wires. The following are known techniques of suppressing excessive current to gate electrodes or emitters in electron source elements (e.g., see patent documents 1 to 4).